I haven't flown for years because I'm scared of flying. Therapy hasn't worked. I may need to fly for my job. Is there any medication that can help?

I'm not sure what therapy you have tried. The best way is to join a group of flying phobics who can help each other. Your doctor also has a range of anti-phobia treatments to consider, from beta-blockers to stop your heart racing to antidepressant drugs that have been shown to work in various phobias, not just fear of flying. One 'treatment' to avoid is alcohol. That may increase anxiety and could make you aggressive and out of control. That's the last thing you want on a plane. Where you sit can help; some people like an aisle seat to lose the feeling of being in the air. Others prefer the window seat, as looking out lessens the impression of being imprisoned in a metal tube. You will know which relates to your fear. Best of luck.

What causes white flecks on fingernails? Is it a dietary deficiency, and why haven't I got them on my toenails, too?

The white spots are tiny areas in which the nail has separated slightly from the skin below. The usual cause is minor trauma to the nail - say from using your fingers in a way that knocks the nail against a hard object. Working at a keyboard may produce them, if you are repeatedly tapping the tips of your nails on the keys. That's one reason why you don't get them on toenails. Few people in Britain who eat normally have a proven dietary deficiency: for those who do, white fingernails would probably be a minor problem.

· Do you have a question for Dr Smith? Email doctordoctor@theguardian.com